The present invention relates to a method for conducting well operations for offshore reservoirs. More particularly, the present invention relates to a system and method for restraining an auxiliary vessel to a compliant platform in support of well operations.
Traditional bottom-founded platforms having fixed or rigid tower structures have been taken to their logical depth limits in the development of offshore oil and gas reserves. Economic considerations suggest that alternatives to this traditional technology be used in deep waters.
Alternative designs have been developed for various configurations of "compliant platforms", e.g., tension leg, compliant tower, and articulated tower platforms as well as floating production systems, which can provide drilling and production facilities in deepwater at costs less than those of traditional fixed platforms.
Further economies and benefits have been provided to the use of such compliant platforms by the recent development of a method for conducting well operations for offshore wells as disclosed in U.S. patent application Ser. No. 624,866 filed Dec. 10, 1990, in which an offshore drilling vessel is docked to the compliant platform which is driven out of substantially vertical alignment over the well site in order to align a drilling derrick of the offshore drilling vessel thereover. Well operations are then conducted from the drilling vessel and the production riser is transferred from the vessel to the compliant platform. This method facilitates supporting well operations with an auxiliary vessel for surface accessible completions which are then hung on a deepwater compliant platform. This permits the use of a compliant platform which does not have to be scaled to accommodate the weight of a major drilling rig and permits well operation facilities supplied by the auxiliary vessel to relocate when those facilities are not needed at the platform.
However, the auxiliary vessel and the compliant platform respond to environmental loads from wind, wave, and current unequally and out of phase. Traditional docking methods will tend to transmit vertical loads from the auxiliary vessel to the compliant platform as the docking elements resist relative motion therebetween. Increasing the capacity of the compliant platform to accommodate such temporary load conditions works against some of the principle benefits of this method of conducting well operations.
Thus, there is a need for a restraining or docking system that better facilitates the use of auxiliary vessels in support of well operations for compliant platforms.